Ion tracer airspeed indicator



Maa'chZS, 1958 B. BOYD ET AL 2,827,786

10N TRACER AIRSPEED INDICATOR Filed July 14, 1953 [0N/ZE!)a ELE C TRODE4;

ATTORNEYS United States Patent O ION TRACER AIRSPEED INDICATOR BemroseBoyd, Cleveland, Robert G. Dorsch, Lakewood, and George H. Brodie,Bedford, Ohio, assignors to the United States of America as representedby the Secretary of the Navy Application July 14, 1953, Serial No.368,018

2 Claims. (Cl. 73-194) (Granted under Title 35, U. S. Code (1952), sec.266) This invention relates to an apparatus for accurately measuringtrue airspeed by a tracer technique by measurement of the time ofpassage of a group of ionized molecules over a known distance withoutinterference with the air flow. in this invention, ion bundles areproduced in a pulse-excited corona discharge and are used as tracerswith a radar-like pulse transit-time measuring instrument in order toprovide a measurement of airspeed that is independent of all variablesexcept time and distance.

Previous known devices have utilized tracer techniques of various typesin the field of dow-visualization and in airspeed measurement. However,these devices have not been generally satisfactory because ofinterference with the ilo'w being measured, particularly in supersonicflow, and because their dependence upon variables other than time anddistance which necessitated their periodic calibration.

Anobject of this invention is to provide a satisfactory instrument formeasuring airspeed at high Mach numbers.

An additional object of this invention is to provide an electronic tmeairspeed indicator which measures true airspeed by timing the passage ofan ion bundle from one detector to another over a known distance andwhich utilizes conventional electronic components.

A further object of ther invention is to provide a measurement ofairspeed which is independent of all variables except time and distance.

A still further object of this invention is to provide an electronictrue airspeed indicator which measures true airspeed by anionization-tracer technique without interfering with the air ilow. Y

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the 4saine becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

Fig. l is a schematic diagram of the subject invention. Fig.l 2 is anenlarged sectional view ofv the needle-point ionizer and its mounting.

Fig.A 3. is a side view, partly in section, of the detector and itsmounting.

The electronic true airspeed indicator, shown schematically in Fig. l,is made up of the following components: an ion signal generatorconsisting of a synchronizer, a high-voltage pulser, and an ionizer 1which isV secured to wind tunnel wall 4; a signal receiver consisting ofdetectors 2 and 3 and an amplifier; a timer connected to thesynchronizer; and an oscilloscope indicator connected to the amplier andtimer. All units of the apparatus operate from a ll7-volt, single-phase,60 cycle power source.

in the apparatus of Fig. l, several possible methods for producing theionization are available including the 4use of' alpha particles,high-speed electrons, ultraviolet trays, X-rays, and various types ofelectric discharge ranging from precorona 'discharge to a spark. For thepurposes of this invention, 'a corona discharge from a needle pointelectrode lgives better results with respect y Patented Mar. 25, 1958responding to the three types of signal modulation: frequency, phase,and pulse-time modulation. The selection of the pulse type of .operationfor this invention allows the ionizer supply to be patterned after thehigh-voltage pulser of a radar transmitter and allows the timer to beVpatterned after the timing circuit of a radar range unit,

thereby `providing an accurate direct measurement of pulse transit timefor the determination of speed in terms of the fundamental units (timeand distance). 'lhe mode of operation of this invention has beenselected so as to allow the .use of conventional electronic circuits,the details of which form no part of this invention. Examples ofcircuits which are suitable for use in the present invention are shownin ydetail in National Advisory Committee for Aeronautics ResearchMemorandum No. R. M. E52C3l, published July 2l, 1952.

In the synchronizer unit, shown schematically in Fig. l, a phase-shiftmaster oscillator provides a signal to each of two channels. ln veachchannel the signal is amplified, squared, and peaked to trigger alow-power blocking oscillator. One channel feeds an externalsynchronizing signal to the timer unit, whereas the other drives -ahigh-power blocking oscillator stage in order to produce thehigh-voltage output trigger pulse. This latter signal lags the externalsynchronizing signal in time phase, and makes it possible to observe onthe oscilloscope indicator the pulse that travels to the receiver probeby direct induction as well as the signal resulting from the passage ofthe tracer ions. Pulse repetition frequencies of 40() and 800 cycles persecond are satisfactory.

The high-voltage pulser of Fig. l is a commonly used radar pulsercircuit. A voltage-doubling rectifier, the amplifier tubes, and theoutput transformer are connected in series to produce the high-voltagepulse. The 'highvoltage pulse transformer is a special unit wound on thepowdered-iron core of -a television liyback transformer. The transformeris insulated with Teon and polyethylene tapes and has a voltage step-upof about l lto 4. The output pulse is bidirectional with a dampedoscillatory transient following the negative half cycle. No attempt ismade to obtain a unidirectional pulse, as experience has shown that abidirectionalpulse gives better results. The eiective width from thefirst positive half-power point to the trailing negative half-powerpoint is 6 tov 8 microseconds. The voltage peaks are of the order of15,000 volts. When Voperating under various air pressures it isdesirable to control the output of the ion signal generator. Thiscontrol may be accomplished either by a voltage divider from ionizer toground or by a variable transformer inA the high voltage supply.

in the ionizer' l shown in Fig. 2, the plastic insulator 6 is formedwith ahead portion 11 which abuts the outer surface of the wind tunnelWall 4- anda shank l2 which is inserted Vin a matching opening in theWall. The screws 7 and 8 pierce the head portion 11 and secure theinsulator in position on the wall. The insulator 6 is center-tapped witha hole 9 which extends almost completely therethrough leaving a thinunpierced section 192 at the inner ace of the shank l2. The ionizerelectriode is in the form of a needle 5 which is inserted in the hole 9'and then forced in until the point 13 pierces the section 1t! and isexposed attire inner face of the shank 12.

Y A e A VIn the detector Fig. 3, brass plug 14 is secured to wall 4 byscrews 17 and V1S with the flange 15 abutting the outer Vsurface of thewall and with shank 16 received in a matching opening therein. Aperipheral groove-[17 is formed around shank 16 approximately midway thelength thereof and forms a retaining seat for an O-ring'seal 1S. Acentral Vopening 31 is formed in the outer surface 'of the flange i anda hole 30 extends from the bottom of opening 31 throughout the length ofshank 16. The pickup consists ofV an electrode 19 and an insulator 20assembled in coaxial configuration in hole 30 and ending flush with theinner surface of the shank 16, the end of the electrode vbeing exposed.The opposite end ofA electrode 19 is .received in holder 21 which isconnected to the tube receptacle (not shown) for tubeZS. Thedetectorhousing 22 contains the electrode Vholder 21'and the input tube 28,which is a type 9002, connected as a cathode follower. The input gridresistor 29 is 1.5 megohms, which gives a low time constant so that thevoltage developed on the Vinput grid is proportional to the inducedcurrent rather than tothe induced charge. The forward end of housing -22is received in opening 31 and the rearward end is open to receive tube28V. The lateral extension 23 acts as a support for the leads from thetube receptacle and ends in a clamp 24 which secures socket 25 in place.The `cable 27 ends in a mating plug 26 which is secured to ,the socket25 by the nut 32. For use with the interdetector method of measurement(using the transit time and distance from one detector to another) inorder to more closely approximate the conditions of measurement at apoint, the detector of Fig. 3 may be modified by replacing the singleelectrode Vand type v9002 tube with a type 616 dual triode and two,electrodes mounted just 1/2 inch apart inthe same plug, Ythus providinga transit distance of only 1/2 inch. Y

The receiver amplifier is a video amplifier with a pass band of about800 kilocycles and which utilizes triodes' vin `order to handle largersignal amplitudes. The signal Afrom the detector is developed across a39,000 ohm cath- Aode resistor returned to a negative bias supply inorder to extend the dynamic operating range. Two triodes (type 9002) areused in the input in a direct-coupledrstage with a high plate load and'alow cathode-follower output load resistor. Output to the indicator istaken through capacitive coupling from the cathode of the final stage.

The indicator used inthe system is a commercial oscilloscope withVprovision for a driven (single) Vsweep with .external synchronization.jand indexing'are possible including circular sweep with radialdeectiom-Z-axis blanking orV intensification, various' -forms ofelectronically generated cursors or time Y -markers, and so forth,but'the orthogonal presentation and fixed lmechanical index are entirelyadequate when Y- used with a delayed and expanded sweep.

The Vtimer is a commonly used radar timing circuit .il f .and consistsof a screen-coupled phantastron used in conjunction with appropriatepulse-shaping circuits. The pulse from the synchronizer triggers'thephantastron timedelay circuit. After a delay time determined by thecontrol setting, a pulse is produced that triggers the driven sweep inthe indicator. Thus the position of any signal with respect to theindicator index is determined by the phantastron control Vsetting inconjunction with the indi- .cator centering control. The time intervalbetween two .signals maybe obtained by setting first one signal then theother'toY the index whileV holding the centering control fixedV andnoting the difference between the delay-times corresponding to thecontrol-dial readings. Calibration of the control dial is accomplishedby means of an interval timer connected in such a manner that both theinterval timer and the time-delay unit can be started by the same,applied pulse, and the timer is stopped by the output pulse L.from thedelay unit. Y Y j In the operation of the present invention, theVsynchro- Ynirer generates two synchronized pulse signals that triggerVarious' types of indication the driven sweep of the indicatoroscilloscope and the high-voltage pulser, respectively. The high-voltagepulser supplies a pulse of 7 to 10 microseconds duration andapproximately 15,000 volts peak to the ionizer. An ion 5 bundle isformed in the air stream opposite the ionizer during its period of pulseexcitation and is carried downstream by the air flow. A signal isVVproduced in the receiver by induction when the ion bundle passes eachdetector. A pulse also appears in the receiver simultaneously with theionizer excitation by direct induction from the ionizer. A fixed timedelay is incorporated in Y the pulse channel from the synchronizer tothe high-voltage pulser for the purpose of allowing the direct pulse tobe viewed on the indicator within the sweep rangeof the timer. Thetimer, a variable time-delay circuit-inserted between the synchronizerand the indicator sweep, enables Ythe operator to position the ionsignal from any detector or the direct signal from the ionizer under theindicator `inderx. The crossover or point of zero signal amplitudeprovides a measurement point that can be accurately located. One of thetwo detectors Vis connected to the amplifier and a reading is taken;then the other detector lis connected to the amplifier and anotherreading is taken. The dierence between the readings of a calibrated dialon the timer for any two of these signals gives the transit time betweenthe correspondingV positions.

The primary use of the present invention is in conjunction with the wallof a wind tunnel, however, a somewhat more general alternate use iscontemplated in which 30-the ionizer and detectors are mounted in astreamlined :housing of known ow characteristics for use in makingYmeasurements at points remote from a wall such as near the center of alarge wind tunnel or on an aircraft.`

A In addition to the primary application, that is, toV pro- Y, 'videmeasurements vwithout introducing shock waves in f A'supersonic'iiow,flush instrumentation may be advantageous in situations where itisdesirable to reduce the drag caused by conventional sensing devices ortheir supports,

where instrumentation is adversely affected by high tem- 40 `lperaturesor erosion, or where its presence may cause increased ice accumulation.

Obviously, many modifications and variations of the :present inventionare possible in the light of the above teachings. It is, therefore, tobe understood that within the scope ofthe appended claims the inventionmay be practiced otherwise lthan as specifically described. r[heinvention described herein may be manufactured hand used by or for theGovernment of the United States ofrA'merica-for governmental purposeswithout the pay- Y ment of'any royalties thereon or therefor.

What is claimed is:

1. Apparatus for indicating the speed of an airstream flowing along asurface comprising means for creating `an ion bundle in said airstreamby corona discharge in- `c1uding a needlepoint ionizer mounted flushVVwith said surface, a high-voltage pulser connected to said ionizerYsaid detectors, and indicator means connected to the .other output ofsaid synchronizer and to the output circuit means of said amplifier;whereby Vto measure'the time 5 j Y interval for lsaid ion bundle totravel from said first de- AYtector to said second detector.

2. Apparatus for indicating the speed of 'an'.airstream Y gowing alongVa surface comprising means for creating .ion bundles by a coronadischarge including a needle- :pointionizer mounted fiush with saidsurface, a high- 'lvoltage pulser connected to said ionizer andsupplying high-voltage pulses of short duration to said ionizer; aamplifier; whereby to measure the time interval for said synchronizerunit having two outputs, one of said outputs ion bundle to travel fromsaid first detector to said secbeing connected to said high-voltagepulser; measuring ond detector.

means including rst and second induction-type detectors u mounted inspaced relation iiusli with said surface down- 5 References Cted m theme of thls Patent stream from said ionizer; said arnplier having inputUNITED STATES PATENTS circuit means and output. circuit means; means forse- 2,569,974 Campbell Oct' 2 1951 lectively connecting said input meansto said detectors, 2,619,836 Downing De@ 2, 1952 and indicator meansincluding a driven sweep oscillo- 2,531,242 Metcalf Man 10, 1953 scopeoperatively connected to the other output of said lo 2,637,208 MellenMay 5, 1953 synchronizer unit and to the output circuit means of said2,679,162 Stuart May 25, 1954

